Coating the inside of tubular members or tubulars, such as oilfield pipe, is well known in the art. Coating the inside of the tubular, by applying a material to the inside diameter or inside surface of the tubular which has been heated previously, is used to prevent corrosion and erosion of the inside surface. Additionally, pipe are often coated in order to reduce friction of the inside surface, as pipe that have been coated require less pressure to pump fluid therethrough, due to the reduced friction.
With recent advances in material science and increased demand for deeper and wider wells, downhole pipe lengths and diameters are increasing. The increased pipe lengths have limited the usefulness of prior coating devices, as these coating devices are unable to provide a uniform interior coating over an extended pipe length or a large pipe diameter. Despite the improvements in powder coating technology, problems of uneven coating thickness or gaps of bare metal on the inside surface of tubular goods have persisted.
Some existing devices have relied on introducing an excessive amount of coating material in order to ensure that the entire interior surface is coated. This procedure includes a thick application of material to the interior of the tubular, which can result in a coating layer that is too thick at one end and too thin at the opposite end. Furthermore, these existing coating devices are not adjustable to tubulars having different lengths and/or diameters. As such, each different pipe size or length requires a different volumetric flow rate therethrough, during coating operations, to maintain the desired powder velocities through the pipe for optimal coating formation.
Changes in pressure within the pipe during coating operations can also cause changes in the velocity of the coating material particles. A thick coating at the load end can result, where the particles have a long dwell or residence time upon initial loading. In addition, just downstream of the load end, a zone of reduced coating thickness can result from the sudden increase in particle velocity. Further, a zone of increasing coating thickness, toward the discharge end of the pipe, can result as the velocity of the particles through the pipe is reduced due to friction and decreased pressure. If increased air pressure is used to compensate for this action, the powder particles will have a greater velocity and will tend to pass through the discharge end without sufficient residence time to melt on the pipe wall, resulting in yet another zone of decreased film thickness. The number of bare metal gaps also tends to increase within the zone of decreased coating or film thickness.
Additionally, weld splatter inside the tubulars, which are manufactured with welded seams, is a common source of coating problems. Specifically, as some weld splatter is not removed when the pipe is cleaned prior to applying the coating, the splatter becomes part of the interior of the tubulars. Previous methods and devices for applying coating to the insides of tubulars are unable to sufficiently cover the bumps and cavities caused by weld splatter because of the improper rates of tubular rotation or improper powder velocities through the tubular.
Yet another drawback of previous devices is that they were unable to ensure constant rotation speeds for variously sized pipe. These previous devices are not automatically adjustable to tubulars having different diameters, wherein each differently sized diameter of the tubulars can rotate at a different speed to cause non-uniform rotation and application.
A further drawback of previous devices is that they rely on a human operator for controlling each step of the coating operations, which results in significant time delays over extended periods of operation.
Therefore, as the previous devices are totally or partially ineffective and deficient in coating the inside surface of tubulars, there is a need to provide improved apparatus and methods for uniformly applying a powdered coating material to the interior of tubulars, regardless of the diameter and/or length of the tubulars.
There is a need for providing a coating device that is adjustable to different tubular diameters, wherein the coating device can be adjusted to supply the necessary volumetric air flow rates into the tubulars to generate and maintain desired powdered coating material velocities during coating operations over the entire length of the tubulars, including tubulars having an extended length.
There is a need in the art for providing a coating device which rotates tubulars, no matter what their diameter, at a constant, predetermined speed.
There is also a need for providing a coating device that can automate each step of the coating operations, minimizing time delays between each phase of the coating operations.
Embodiments usable within the scope of the present disclosure meet these needs.